Commercial and residential buildings employ a variety of different building equipment components. Examples of typical building equipment components include heating and cooling equipment such as furnaces, boilers, heat pumps and the like. Other examples of typical building equipment components include water heaters, air exchangers and other ventilation equipment and similar equipment. A variety of HVAC equipment employ dampers, zone valves and the like.
In particular, water heaters are used in homes, businesses and just about any establishment having the need for heated water. Water heaters often heat water using the simple “heat rises” principle. In operation, water heaters typically heat cold or ambient temperature water entering at or near the bottom of the water heater to a desired temperature using a gas-fired burner, an electric heater or some other heater element. During a heating cycle, the cold or ambient temperature water at or near the bottom of the water heater becomes hotter and begins to rise towards the top of the water heater. Cooler and denser water, once on top of the water being heated, falls toward the bottom of the water heater so that it can be heated or reheated to the desired temperature. After the temperature of the water at the bottom of the water heater reaches a certain desired temperature, the water heater typically stops heating the water for a period of time.
When demand for hot water arises (e.g., someone turns on a faucet to run a shower), fresh, cold or ambient temperature water enters the water heater and “pushes out” or supplies the hotter water at or near the top of the water heater. When a sufficient amount of the hotter water exits from the top of the water heater so that the fresh, cold or ambient temperature water entering the bottom causes the temperature of the water at the bottom of the tank to drop below a set point temperature, the water heater typically turns on and repeats the heat cycling described above.
A conventional water heater typically has at least one heating element or “heater,” such as a gas-fired and/or electric burner. To take advantage of the “heat-rises” principle, the heater is typically located at or near the bottom of the water heater tank. Each water heater typically also has at least one thermostat or controller for controlling the heater.
To facilitate the heating of water, the controller often receives signals related to the temperature of the water. When these signals indicate that the water temperature is below a first set point, for example, when the water temperature is below 120 degrees Fahrenheit, the controller turns on the heater and the water at or near the bottom of the water heater begins to heat. After some time, the temperature of the water at the bottom of the water heater will increase to a second set point, which, for example, may be about 140 degrees Fahrenheit. When the water temperature at the bottom of the tank is indicated as being greater than the second set point, the controller typically causes the heater to reduce its heat output or, alternatively, causes the heater to turn off. The heat cycle begins again when the temperature of the water at the bottom of the water heater drops below the first set point.
Some water heaters rely upon a single water temperature sensor, while others employ two water temperature sensors. In some cases, using two water temperature sensors, such as one at or near the top of a water heater and a second at or near the bottom of a water heater, may provide improved temperature control resulting in energy savings, higher hot water capacity, and greater potential safety.
As described above, the hottest water in a water heater may typically be found at or near the top of the water heater tank. As a result, the water at or near the top of the water heater tank may be substantially hotter than the water at or near the bottom of the water heater tank, such as where a single water temperature sensor may be located. This means that the water at or near the top of the water heater tank may be hotter or even substantially hotter than a lower, safer temperature, such as may be indicated by the water temperature sensor at or near the bottom of the water heater tank.
Thus, in some cases a water heater includes a second temperature sensor that may be positioned at or near the top of the water heater tank, in order to provide the controller with information pertaining to the water temperature at or near the top of the water heater tank. The second temperature sensor positioned at or near the top of the water heater tank may also be useful in reducing or eliminating stratification, which may occur as a result of frequent small hot water withdrawals from the water heater tank.